This invention relates to a porous, sterile hydrophobic polytetrafluoroethylene (PTFE) membrane laminate product and to a process for making the same. More particularly, this invention relates to a sterile PTFE microporous or ultrafiltration membrane laminate formed from a hydrophobic PTFE membrane directly laminated to a porous web substrate which is mechanically resistant to pressure.
By the term "sterile" as used herein is meant a laminate which is rendered sterile by gamma radiation.
In many applications of membrane technology, it is desirable to utilize a membrane filter which is mechanically strong, is thermally stable, is relatively inert chemically and is insoluble in most organic solvents. It is desirable to provide such membranes which are also hydrophobic so that they are not wet under pressure by solutions including solutions that contain surfactants. Hydrophobic membranes are not permeable to aqueous solutions even under moderate solution pressures and thus such membranes are useful as a seal to aqueous solutions while, at the .same time, being permeable to gases.
Prior to the present invention, PTFE membranes have been sterilized with ethylene oxide gas or by gamma radiation. The use of ethylene oxide is undesirable since the gas is toxic and causes a pollution problem. Gamma radiation also is undesirable since it reduces the mechanical strength of the PTFE membrane so that it is not capable of withstanding moderate pressure in the forward or reverse direction of filtration. Therefore, it would be desirable to provide a sterile PTFE membrane capable of withstanding elevated pressures while avoiding the use of toxic sterilizing compositions.